In conventional internal combustion engines, the intake and exhaust ports of each cylinder are controlled by poppet valves or the like which in turn are actuated by a camshaft driven by the crankshaft. Typically, the poppet valves are biased to a closed position relative to their respective ports and are positively actuated to an open position against the bias of the valve spring by cam lobes on the camshaft. The camshaft is usually drivingly engaged with the crankshaft by gearing so that the speed of the camshaft has a constant, fixed relationship to the speed of the crankshaft, e.g., the gearing between the crankshaft and camshaft may be such that the camshaft is driven at one-half the speed of the crankshaft. During rotation of the crankshaft, the various poppet valves move between their open and closed positions in a sequence and at speeds determined solely by the mechanical construction of the camshaft. All of the valve events, whether of an intake or exhaust poppet valve, are fixed mechanically with respect to the speed of the crankshaft and with respect to the angular position of the crankshaft with respect to some reference point. As used herein, the term "valve events" is meant to include the sequence of operation of the poppet valves, the crankshaft position at which each poppet valve opens and closes, the opening and closing rate of each poppet valve, the amount of opening of each poppet valve, and the dwell time of each poppet valve position.
It is apparent and has long been recognized that improved fuel economy, improved performance, and possible reduction in emissions could result if the valve events were not fixed mechanically with respect to the crankshaft speed and position, but instead could be made variable in accordance with the power requirements, independently of crankshaft speed.
Some modifications have been made to date in the valve events of prior art engines to obtain split engine performance by selectively disconnecting certain of the intake and exhaust poppet valves when the engine is at idle or cruising speed. See, for example, U.S. Pat. No. 3,974,455 of June 22, 1976, and the copending application Ser. No. 699,612 of Edgar R. Jordan, entitled "Valve Deactivator For Internal Combustion Engines", filed June 24, 1976, now U.S. Pat. No. 4,114,588. However, in the split engine arrangements, the only variation of the valve events possible is to selectively deactivate cylinders of the engine so that, for example, an eight cylinder engine can operate on four, six or eight cylinders depending on the engine load. The individual cylinders are either completely deactivated, or are completely activated. When activated, the intake and exhaust valves of the cylinder are again mechanically coupled to the crankshaft through the camshaft. This type of system is also discussed in the article by Larry Givens entitled "A New Approach to Variable Displacement", Automotive Engineering, May, 1977, Volume 85, No. 5, pages 30-34.
U.S. Pat. No. 4,009,695 of Mar. 1, 1977 discloses a programmed valve system for internal combustion engines utilizing two stage servo-valves for actuating the poppet valves controlling the intake and exhaust ports of the engine cylinders. The servovalves are mounted directly above the stem of the associated intake or exhaust poppet valves. When pressurized, a rod of the hydraulic servo-valve actuator extends to open the poppet valve against its valve spring, and the valve spring causes the valve to close when hydraulic pressure is removed permitting the rod to retract. The patent also discloses a computer for determining the signals to be transmitted to each of the servo-valves for actuating the intake or exhaust valves in accordance with varying conditions. The servo-valve actuator has one pintle controlled by a solenoid for admitting fluid into a chamber and another pintle controlled by another solenoid for exhausting fluid from the chamber so that the piston extends and retracts from the servo-valve in response to the admission and exhaustion of fluid from the chamber.